The is_file() check got lost during the refactoring in
d855b470.

Change-Id: Ia1688099a7ccd32667562e8c7f83fd54bb669f4a
Resolves: #80354
Releases: master, 7.6
Reviewed-on: https://review.typo3.org/52100


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Josef Glatz <josef.glatz@typo3.org>
Tested-by: Josef Glatz <josef.glatz@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>